Checking Balanced Parentheses (an Application of Stacks)

In this lesson you will learn how to check that brackets are balanced using a stack in C#, a practical application of the stack data structure. This is for anyone searching for "C# balanced parentheses stack".

With a stack (last in, first out) you can push opening brackets such as ( and [, then check each closing bracket against whatever is on top. That is how bracket matching works.

The sample code keeps the opening bracket for each closing bracket in a Dictionary named pairs, pushes with stack.Push() on an opening bracket, and checks the top of the stack on a closing one. If the stack is empty once everything has been processed, the brackets are balanced.

A common stumbling block for beginners is handling several kinds of bracket at once (round, square, and curly mixed together). Counting openings and closings is not enough - you also have to confirm they nest in the right order.

The same idea is genuinely used behind editor auto-completion and code syntax checking. Plenty of similar tools check that HTML opening and closing tags line up correctly.

📖 Reference code

using System;
using System.Collections.Generic;

class Program {
    static bool IsBalanced(string str) {
        var stack = new Stack<char>();
        var pairs = new Dictionary<char, char> { { ')', '(' }, { ']', '[' }, { '}', '{' } };
        foreach (char ch in str) {
            if (ch == '(' || ch == '[' || ch == '{') {
                stack.Push(ch);
            } else if (ch == ')' || ch == ']' || ch == '}') {
                if (stack.Count == 0 || stack.Pop() != pairs[ch]) return false;
            }
        }
        return stack.Count == 0;
    }

    static void Main() {
        Console.WriteLine(IsBalanced("(a[b]{c})"));
        Console.WriteLine(IsBalanced("(a[b)]"));
    }
}

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🧪 This site can't compile or run C# directly, so it checks on the spot whether what you typed matches the reference code (scoring happens entirely in your browser — nothing is sent anywhere).